1. Field of the Invention
The present invention relates to a PC Card applied to a CardBus which is used under PCI bus architecture. It relates in particular to an interface circuit for use where a device complying with a PCI bus connects to a CardBus, and to a PC Card having this which is capable of being connected to a CardBus.
2. Description of the Related Art
PCI (Peripheral Component Interconnect) buses are high-speed buses standardized as local buses for use in personal computers, and offering operational stability and extendability together with abundant bus and system control functions. PCI buses are 32-bit wide buses synchronised with a 33 MHz clock, and are capable of achieving transfer speeds up to a maximum of 133 Mbyte/sec. To these PCI buses, PCI cards with SCSI controllers, graphic accelerators and other PCI devices can be connected directly via a PCI connector.
Meanwhile, there are also CardBuses, which have been standardized with a view achieving the same functions as a PCI bus by means of a PC Card. 16-bit PC Cards have been available for fitting to 16-bit ISA buses, and CardBuses has been standardized so as to enable PC Card with business card size to be fitted to PCI buses. Thus, PC Cards for use in CardBuses, i.e. 32-bit PC Cards, are connected to the PCI bus via a PCI-CardBus bridge within the CardBus below the bridge.
PC Cards for use in CardBuses, ie 32-bit PC Cards (hereinafter for the sake of simplicity referred to as `CardBus PC Cards`), offer the same facilities for SCSI controllers, graphic accelerators and other devices as the PCI devices. The only difference is that CardBus PC Cards are configured as cards of business-card size rather than for fitting on to a printed substrate as with PCI devices.
However, the above-mentioned CardBuses differ from PCI buses in two respects. Firstly, while the power supply for CardBuses is restricted to 3.3 V, PCI buses are compatible with both 3.3 V and 5 V. Secondly, CardBuses make use of card attribute data known as CIS (Card Information Structure) in order to assign their resources. This CIS constitutes the PC Card attribute data which needs to be communicated to the system side when the CardBus PC Card is inserted. Thus, in the case of a CardBus PC Card complying with a CardBus, a CIS pointer register showing the memory area where the CIS is stored is provided within the configuration space thereof. It may be added that in the example to which the present aspect pertains, as will be explained later, the configuration space is a memory area having a plurality of configuration registers.
Meanwhile, in case of a PCI device connected to a PCI card via a PCI connector, configuration space is provided in the same manner and a CIS pointer register as above is prescribed as an option register, but hardly any PCI devices have one packaged.
As has been mentioned above, an SCSI controller, graphic accelerator and other facilities are packaged with a PC Card as PCI devices (LSIs with PCI interface), which can be connected to the PCI bus via a PCI connector. Further, the above SCSI controller, etc. are integrated within the PC Card as an LSI and connected to the CardBus via a CardBus connector. Thus, while the function is the same, one complies with a PCI bus while the other complies with a CardBus. The above two points constitute the principal differences, but a PCI device complying with a PCI bus can not be used by being mounted on PC Card without modification.
It is an object of the present invention to provide an interface circuit which allows a PCI device to be used as an LSI mounted within a CardBus PC Card.
It is a further object of the present invention to provide a PC Card with an interface circuit of this type.